This-invention relates to an end mill formed of a tungsten carbide (hereinafter simply referred to as "WC")-base sintered hard alloy having high strength and high toughness, as well as excellent wear resistance.
Conventionally, an end mill as a cutting tool is widely known, which is formed of a WC-base sintered hard alloY, and the WC-base sintered hard alloy comprises a binder phase including a Co-base alloy, and a hard disperse phase consisting essentially of WC in the following proportions:
binder phase: 10.5-16.5% (hereinafter percentages are weight percentages throughout the specification), and PA0 hard disperse phase: 83.5-89.5%. PA0 binder phase: 6-23%, and PA0 hard disperse phase: 77-94% PA0 Cr: 1-5%, PA0 W: not more than 5%, and PA0 disperse phase in proportions of: PA0 binder phase: 8-12%, and PA0 hard disperse phase: 88-92%.
The binder phase has a composition of 2.5-11.6% of vanadium (V), and the balance of Co and inevitable impurities. As the starting material for V, which forms a solid solution in the binder phase, is used a powder of vanadium carbide (hereinafter simply referred to as "VC"), which is mixed with the other starting materials. During sintering, VC is decomposed and the vanadium component is dissolved into the binder phase to form a solid solution therein, which acts to suppress the growth of WC particles dispersed therein rather reduce the size thereof into a mean grain size equal to or smaller than 0.5 .mu.m to thereby enhance the hardness and hence improve the wear resistance.
Although in the conventional end mill formed of the above-described WC-base sintered hard alloy, the WC-base sintered hard alloy has enhanced hardness and hence improved wear resistance due to the fine WC particles, its toughness is lowered accordingly. Therefore, if the end mill is used for cutting very hard materials or cutting by high-speed feeding, it is liable to break or be chipped at a cutting edge thereof due to insufficient toughness and strength, and hence it has a rather short life.